A system for probing properties of a trailer towed by a towing vehicle in a heavy-duty vehicle combination. The system comprises at least one torque generating component for inducing movements of the trailer relative to a yaw axis of the trailer; a control unit configured to, during driving of the vehicle combination, activate the torque generating component and apply a pre-determined control action to the torque generating component so as to excite oscillations of the trailer; and at least one detection unit configured to detect the resulting oscillations of the trailer, wherein the control unit is configured to, based on the detected resulting oscillations, determine one or more properties of the trailer. The invention also relates to a probing method.